Boston’s astounding month of snow a 1-in-26,315 year occurrence

A crew clears the sidewalk at the Maverick subway station in Boston on Feb. 15. (Michael Dwyer/AP)

Tuesday marked exactly one month since Boston’s epic stretch of astronomical snowfall totals began. The city’s 30-day snowfall record was broken by almost three feet, and so far February has delivered 10 times the average amount of snow for the month.

With 1.9 inches of fresh accumulation as of 9 a.m. Wednesday, a total of 101.8 inches of snow has fallen in Boston so far this winter, nearly all within the past 30 days. It’s the fastest the city has ever reached 100 inches in a single season, and puts Boston on pace for its snowiest winter in history. The all-time record of 107.6 inches was set in 1995-1996, meaning the current winter is now fewer than six inches away.

Inspired by the city’s off-the-charts winter so far, University of Oklahoma meteorologist Sam Lillo mused on Twitter, “after absolutely destroying the past record, might as well go after simulated ones now right?”

That set him on a statistical coding spree aimed at generating a million-year synthetic dataset of plausible winters based on actual historical data in Boston back to 1938. To do this, he parsed through every three-day period (to maintain meteorological plausibility and prevent the possibility of back-to-back-to-back 20-inch snowstorms) and then randomly generated a set of hypothetical winters consistent with the city’s climate history. His analysis shows that given a static climate, Boston can expect a winter with a 30-day stretch like this one only once approximately every 26,315 years — 38 out of a million.

For comparison purposes, I asked Lillo to run the same calculation for D.C.’s “snowmaggeddon” winter of 2009-2010. His conclusion was that that winter was only a 1-in 238 year occurrence, a whopping 110 times more likely than Boston’s month of winter misery.

Statistical probability analysis of Washington’s 30-day snowfall total during the winter of 2009-2010. (Sam Lillo)

Of course the climate isn’t static. For example, Chris Mooney has recently argued that abnormally warm waters off the East Coast this winter are boosting the moisture availability in snowstorms, and making new snowfall records more likely.

“It’s very hard to actually have any perspective when we are so far beyond the previous record right now,” Lillo said. Hence the statistical analysis.

That means some incredible records continue to be broken. Boston is on pace for near-record snowfall for Anchorage, and has already eclipsed the 30-day snowfall record for Buffalo — a city known for its intense lake-effect fueled snowstorms, like the one just a few months ago that shut down the region.

In a phone conversation on Tuesday, Lillo told me he was “very, very surprised” at his results. “I mean, I knew it was a rare case. Just the fact that we absolutely destroyed the previous record is a testament to how significant of a situation this was.”

“There’s something to be said for getting stuck in a pattern … but this is incredible from a statistical standpoint,” Lillo said. “Boston was just literally in the bullseye for every single storm.”